“Brake-by-wire” braking systems are becoming ever more common in automotive engineering. Such braking systems often comprise a pedal decoupling unit, which is connected to a brake master cylinder on the inlet side, so that an actuation of the brake pedal by the driver in the “brake-by-wire” operating mode does not lead to direct actuation of the brake master cylinder by the driver. Instead, in the “brake-by-wire” operating mode the brake master cylinder is actuated by an electrically controllable pressurization device, in other words actuated “separately”. In order to give the driver an agreeable pedal feel in the “brake-by-wire” operating mode, the braking systems usually comprise a brake pedal feel simulation device. In these braking systems the brake may also be actuated on the basis of electronic signals without any active involvement on the part of the driver. These electronic signals may be delivered, for example, by an electronic stability program ESC or a distance control system ACC.
The international patent application WO 2008/025797 A1 discloses such a braking system. In order to be able to dispense with an elaborate and inefficient intermediate storage of hydraulic servo energy, it is proposed that the fluid needed for electrical control of the input pressure in an intermediate chamber used for actuation of the brake master cylinder be held ready at zero pressure in the pressurization device and subjected to a higher pressure as required. The pressurization device used for this purpose is formed by a cylinder-piston arrangement, for example, the piston of which can be actuated by an electromechanical actuator. A method for controlling the braking system, in particular the pressurization device, is not described.
The object of the present invention, therefore, is to provide a method for controlling an electro-hydraulic “brake-by-wire” braking system having an electrically controllable pressurization device, having a cylinder-piston arrangement, the piston of which can be actuated by an electromechanical actuator, the method affording a considerable improvement of the pressurization device functions.
According to the invention this object is achieved by a method as and a device in accordance with this invention.
A closed or open-loop brake pressure control function is preferably taken to mean an antilock control (ABS), a traction or wheel slip control (TCS, ASR), an electronic stability program (ESP, ESC, yaw moment control) or a driver assist function such as, for example, ACC, HSA, HDC etc.
The method according to the invention is advantageously performed in a braking system for motor vehicles, which in a so-called “brake-by-wire” operating mode can be activated both by the driver of the vehicle and also independently of the driver of the vehicle, which is preferably operated in the “brake-by-wire” operating mode and which can be operated in at least one reversion operating mode, in which operation is only possible by the driver.
The wheel brakes are preferably connected to the hydraulic pressure chamber of the cylinder-piston arrangement. An electrically activated inlet valve, which serves for hydraulically isolating the wheel brake from the pressure chamber, is preferably arranged between a wheel brake, in particular each wheel brake, and the pressure chamber. A brake master cylinder, which serves to actuate the cylinder-piston arrangement, is advantageously arranged between the pressure chamber of the cylinder-piston arrangement and the inlet valve(s).
A wheel brake, in particular each wheel brake, can preferably be connected to a brake fluid reservoir via an electrically activated outlet valve.
It is likewise preferred that the hydraulic pressure chamber of the cylinder-piston arrangement be connectable to a brake fluid reservoir via an electrically activated valve.
The braking system preferably comprises a brake master cylinder, which can be actuated by means of the electrically controllable pressurization device and to which wheel brake circuits are connected, and a hydraulic pedal decoupling unit arranged between a brake pedal and the brake master cylinder.